Vehicular exhaust gas treatment systems are used to treat the exhaust gas from an engine of the vehicle. The exhaust gas emitted from a diesel engine, is a heterogeneous mixture that contains gaseous emissions such as carbon monoxide (“CO”), unburned hydrocarbons (“HC”) and oxides of nitrogen (“NOX”) as well as condensed phase materials (liquids and solids) that constitute particulate matter. Catalyst compositions, typically disposed on catalyst supports or substrates that are disposed within the exhaust gas treatment system are provided to convert certain or all of these exhaust gas constituents into non-regulated exhaust gas components. For example, diesel exhaust gas treatment systems may include one or more of a precious metal containing diesel oxidation catalyst (“DOC”) converter for the reduction of CO and excess HC, a selective catalytic reduction (“SCR”) device for the reduction of NOX with the assistance of a diesel exhaust fluid (“DEF”), and a diesel particulate filter (“DPF”) device for the removal of particulate matter. When periodic regeneration (or soot oxidation) is required, the DOC will oxidize injected diesel fuel, i.e., hydrocarbons, to generate an exothermic reaction to burn off the accumulated soot inside the DPF. The exhaust system requires a hydrocarbon mixer upstream of the DOC and a DEF mixer upstream of the SCR to provide more uniform reductant distribution of the hydrocarbons and the DEF respectively for effective DOC and SCR operations.
Exhaust gas treatment systems, such as described above, are particularly well suited for treating exhaust gas from diesel engines. However, such complex exhaust gas treatment systems are difficult to package into passenger cars, light duty pick-up trucks, and vans due to limited packaging space available.